The present application relates to monitoring and calculating line sag in electrical power transmission and distribution systems.
Wire conductors in power line sections are typically designed to maintain a certain clearance from vegetation, structures, or other objects, such that a flashover does not occur. Accordingly, designers determine a maximum amount of acceptable sag in connection with the design of power lines, wherein the amount of sag is affected by various factors such as (but not limited to) the temperature of the conductor, ambient temperature, conductor material, weight of the conductor, etc. With more specificity, when power lines are electrically loaded, the temperature of these lines increases as current increases, leading to thermal elongation of the power lines. This thermal elongation results in increased sag per power-line span, which in turn reduces clearance between conductors and objects below.
Recently, devices have been placed locally at specific power line spans to calculate line sag for a span by using local measurements. For example, a mechanical device that measures changes in line tension can be placed at a span of interest. These measured changes in tension can be employed to compute the line temperature at the particular span, which in turn can be utilized to calculate the sag of the power line at the span. In another example, a temperature sensing device has been used to measure surface temperature of the conductor at a specific location on the power line. Again, the sensed temperature can be utilized to compute sag of a power line of the span where the temperature is ascertained.
In still yet another example, video equipment has been placed proximate to a power line span where sag is desirably determined, such that the video equipment is directed towards a reflective target placed on the power-line span. Images generated by the video equipment can then be analyzed to determine sag at this power-line span. In a similar system, it is proposed that a Global Positioning System (GPS) receiver be placed on a certain power line span of interest, such that as the line sag changes the GPS receiver's position in space changes accordingly.
While the use of these systems has proven effective, each of these systems include devices that have been placed locally at a span of interest; therefore, costs are incurred in that installation and maintenance of these devices has to be undertaken at the span of interest. Additionally, power lines may need to be de-energized and taken out of service to install one or more devices of the systems. Still further, such devices are prone to being struck by lightning and are subject to other suboptimal weather conditions.